Recently, the trends for electronic equipment, such as mobile phones, digital cameras and personal digital assistant (PDA), etc. are toward thinner, lighter, and smaller equipment. The structure of a battery, which is used in much electronic equipment, then inevitably decides the weight, energy density, and volume of the battery.
The traditional electrode structure of a battery as shown in FIG. 2a and FIG. 2b includes a positive electrode 30, a separator 31, a negative electrode 32 and a separator 33 overlapping to form an electrode group. Then, at least one of the electrode group is rolled to form a circle, an ellipse or a spiral, as shown in FIG. 2a, within a cylindrical or prismatic case (not shown) for making a battery. Alternatively, a plurality of electrode groups are stacked, as shown in FIG. 2b, within a rectangular case (not shown) for making a battery. Then, an electrolyte is injected into the case to complete a battery.
The positive electrode 30 is usually made of a first metal plate and a positive material coated on both sides of the first metal plate. The negative electrode 32 is usually made of a second metal plate and a negative material layer coated on both sides of the second metal plate. The separators 31, 33 are porous and insulating to separate the positive electrode 30 from the negative electrode 32 so as to avoid forming a short circuit between the electrodes. On the other hand, the separators 31, 33 have many small apertures through which ions pass during the battery charging or discharging process.
The manufacture of a traditional battery is a mature technology. However, it is difficult to roll these overlapping plates during the manufacturing process of the battery. Besides, if each plate does not align with the other precisely, the desired overlapping areas are reduced. Accordingly, the capacity of the battery decreases. Moreover, it may even cause short circuit at the edges of these plates when the worst case happens. Due to the foregoing, there is a need for making high quality and cheaper batteries.